The exhaust gas of diesel engines, gasoline engines, and other internal combustion engines includes, for example, carbon monoxide (CO), unburned fuel (HC), nitrogen oxides (NOx), particulate matter (PM), and other constituents. The internal combustion engines are mounted with exhaust purification systems for removing these constituents. As the method for removing nitrogen oxides, it is known to arrange an NOx storage catalyst in the engine exhaust passage. Further, as the method for removing the particulate matter, it is known to arrange a particulate filter in the engine exhaust passage.
In Japanese Patent Publication (A) No. 2009-257209, an exhaust purification system of an internal combustion engine is arranged in which an NOx storage catalyst and PM filter are provided in an exhaust passage and in which, in an intermediate part between the NOx storage catalyst and PM filter, a second fuel addition valve for feeding fuel to the PM filter, a mixer, and an oxidation catalyst are arranged in that order. It is disclosed that, at the time of regeneration of the PM filter, fuel which is fed from the second fuel addition valve is oxidized at the oxidation catalyst whereby the temperature of the exhaust gas rises and, furthermore, the temperature of the PM filter also rises. Further, it is disclosed that when the processing for NOx reduction for the NOx storage catalyst and the processing for regeneration for the PM filter overlap in timing, before adding fuel from the second fuel addition valve, the temperature of the exhaust gas near the mixer is made to rise to a temperature where the fuel which is added from the second fuel addition valve reliably vaporizes at the mixer.